DIY Doctor

Replace Single Switch With 2 Gang Dimmer for 2 Banks of Lights

Postby lardbodger » Mon Sep 05, 2016 8:34 pm


Apologies if this problem exists already but I searched and found similar but not quite the same.

I have 2 light fittings in my lounge, each has a 4 halogen bulb fitting attached, 4xGU10 in each. There's currently 1 switch which turns both fittings and all 8 bulbs on and off. I want to replace with 2 dimmers so each bank can be dimmed or on or off independently.

In the back of the old switch there are two wires coming in. Each with a red, a black and a yellow/green wire. The yellow/green are wired to the back of the fitting. The black wires were together in a connector block and 1 of the reds was in common and the other in L2 in the switch.

I replaced with a 2 gang 2 way 400W dimmer. The instructions said to wire black to common and red to L2 so this is what I did, separating each wire to one of the two gangs, and leaving the earths as they were.

When I turned on the power, there was a loud pop and spark at the switch and the fuse in the RCD blew.

I'd be grateful for any advice, preferably not just "get an electrician in" but beggars can't be choosers!
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Simply Build It

Postby lardbodger » Tue Sep 06, 2016 5:49 pm

Never mind. I was ignorant. Two wires is one circuit apparently so only one switch possible.
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Postby kbrownie » Tue Sep 06, 2016 10:03 pm

The blacks are neutrals!! Not switch line conductors! That is why they were not terminated at the switch plate. And that is why you got a loud pop, likely fried the dimmer as a result!

You really need to do some research before messing around with electrics. I would also be very surprised if the manufacturers instruction, stated to terminate a neutral across a switch line???

As you have now found, the cables at the existing switch, will only allow for a single gang switch, you will need to pull another cable in, to achieve a double gang set up.
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